In recent years, environmental concerns have become global issues. The auto industry has taken a proactive stance to facilitate environmental reform in the automobile production processes.
Automobile production can be the cause of various environmental problems including global warming, industrial waste, output of volatile organic compounds (VOC) etc. Particularly, since VOC output is mostly caused by car painting processes, there is a demand for an immediate solution.
To prevent corrosion and for aesthetic purposes, the exterior panels of car bodies are generally coated with a multilayer coating film consisting of a base coating film formed of a cationic electrodeposition coating composition, an inter-coating film, and a top-coating film. To reduce VOC, inter-coating compositions and top-coating compositions are more often made of aqueous compositions these days.
Superior finishing appearance and film performance are indispensable, particularly for coating films of automobiles. However, since the existing aqueous coating compositions are used with water as the solvent, the finishing appearance of the resulting coating film is generally unsatisfactory, compared with those formed of solvent-type coating compositions.
For example, Patent Document 1 discloses an aqueous coating composition mainly containing a specific acrylic resin and/or polyester resin, specific polycarbonate resin, and a curing agent. This aqueous coating composition, however, cannot assure a satisfactory finishing appearance. Patent Document 2 discloses an aqueous coating composition mainly containing a specific acrylic resin and/or polyester resin, a specific polycarbonate resin, a curing agent, specific resin granules. This aqueous coating composition is also conducive to a poor finishing appearance of the resulting coating film in some cases, such as poor smoothness etc.